A data cable that goes from a computer to a portble device (MP3 player, digital camera, mobile phone etc). At the computer end is a USB connector. At the device end is a IEEE1394* connector. Close to the device end is a lump in the cable which contains a small circuit board that does the data conversion.

The
board is powered from the PC using the USB cable. The portable device is powered either from its internal cells or from a mains transformer that plugs into a IEEE1394 socket on the plastic lumpy bit in the cable.

Your portable device would be supplied with the following items:
 Mains to IEEE1394 adaptor (country specific). Used to charge your portable device. Would work with any other device that took its power from an IEEE1394 cable.
 IEEE1394 cable to connect your computer (should you have an IEEE1394 socket of it) to the portable device. Will be used to power the device from the computer during data transfers and can be used to charge the portable device.
 USB powered USB to IEEE1394 connector to connect your computer (should you not have an IEEE1394 socket on it) to the portable device. The device is either self-powered or powered by the transformer as described above.

If you've got to this point and you're still asking, "Why do I need this?", or "But don't all portable devices have USB sockets anyway?" please read 'USB Power Supply' (see link) and the following paragraph.

The aim behind this idea and that of 'USB Power Supply' is to create a standard power supply for future portable devices. I'm sick of carrying a separate phone charger, digital camera charger and buying batteries all the time for my PDA and MP3 player. I'm sure you are too.

*aka Firewire, iLink
____________

Possible enhancements:
Travel adaptor - Multi-voltage version of the adaptor.
Multi adaptor - Able to charge/power several devices simultaniously.

phoenix: Um, yes. That's what this is about. Rather than create something new I'm suggesting using the IEEE1394 standard *as* a standardised mains transformer. This device is something that popped into my head as being useful should this happen.

As I stated in the idea and to lessen the need to read to the end, "The aim behind this idea and that of 'USB Power Supply' is to create a standard power supply for future portable devices. I'm sick of carrying a separate phone charger, digital camera charger and buying batteries all the time for my PDA and MP3 player. I'm sure you are too."

I don't get this idea. It seems to want a standard for supplying power to small electronic devices (which we now have, with USB) but it seeks to accomplish that by enabling USB hosts to communicate databut not powerwith FireWire peripherals (which is itself something that would need serious elaboration to be plausible, with the protocols being so fundamentally different).